Comprehensive LDV
Comprehensive LDV (CompLDV, see our article in MST) is an advanced measurement technique that was
developed and proven by AUR personnel. The technique is loosely based upon the
dual-beam LDV concept, but with improvements to measure particle measurement volume
position and acceleration in addition to the usual measurements of velocity vectors.
The AUR CompLDV is the only measurement system that is
capable of measuring three-components of velocity, position,
and acceleration over the dynamic ranges that high Reynolds
number turbulent flows exhibit. The measurements are resolved
in both time and space for a wide range of flow scales, even in
very near-wall regions of bounded flows
The CompLDV technique is a new tool for researchers seeking to
understand fundamental phenomena related to drag, flow-
generated noise, and turbulence structure in a wide range of
flows.
Capabilities
- Highly resolved near-wall turbulence measurements
- The CompLDV is the only instrument in the world that
can deliver high Reynolds number velocity profile
measurements in 3-D flows to within 10s of microns from a
surface.
- Using advanced instrument configurations and custom,
exclusive signal processing techniques, the CompLDV
sets a new standard in near-wall flow characterization.
- Velocity spectral measurements
- All velocity components are measured at very high data rates (40kHz in
low-speed flows). This allows very near-wall characterization of the
frequency content of turbulent flows.
- Measurements of cross-spectra are possible and may be used to explore the
coherency of pairs of velocity components. These measurements indicate the ranges of frequencies
where significant anisotropy exists. No other technique can be
used this effectively for near-wall velocity spectral studies.
Velocity gradient statistics measurements
- Research has shown (Lowe and Simpson 2008a) that time-series data from the CompLDV may be used
to estimate the instantaneous velocity gradients in the flow.
Velocity-acceleration statistics measurements
- The advanced optics configuration and signal processing techniques for the
CompLDV give instantaneous acceleration measurements in turbulent flows.
- In particular, the fluctuating velocity/acceleration correlation
is a direct measurement of Reynolds stress transport terms.
- When used with the dissipation estimates available from both
the velocity gradient tensor and spectra, velocity/pressure
gradient correlation measurements are possible.
